Detection Of Sulfur Compounds Research Articles

Contribution of the novel sulfur-producing adjunct Lactobacillus nodensis to flavor development in Gouda cheese

We assessed the efficacy of Lactobacillus nodensis CSK964 as an adjunct culture in Gouda cheese under various industrial conditions. We set up 4 different systems: a direct vat inoculum with and without adjunct using the calf rennet Kalase, and an undefined bulk starter culture with and without adjunct using the microbial rennet Milase (both rennets from CSK Food Enrichment, Ede, the Netherlands). During ripening, we subjected the cheeses to the following analyses: viability of starter and adjunct cells, composition, proteolysis, and flavor development by detection of sulfur compounds and descriptive sensory analysis. In general, the presence of Lb. nodensis increased secondary proteolysis and influenced cheese flavor, particularly in relation to volatile sulfur compounds; hydrogen sulfide and methanethiol were present in higher abundances in cheeses containing Lb. nodensis. The primary starter also influenced the range of volatile sulfur compounds produced. Methanethiol and dimethyl disulfide were more abundant in the nisin-producing direct vat inoculum cheese with adjunct; hydrogen sulfide was more prevalent when bulk starter culture was used with Lb. nodensis. Sensory analysis revealed that the direct vat inoculum cheese with adjunct scored significantly better in terms of smell and taste than the direct vat inoculum cheese without adjunct and lacked the dominant sulfur flavors of the bulk starter cheese with adjunct. Subsequent analysis using lead acetate paper and modified motility broth as indicators of hydrogen sulfide production confirmed that Lb. nodensis produced hydrogen sulfide in broth and in the cheese matrix. This study suggests that the inclusion of Lb. nodensis as an adjunct culture can significantly alter the flavor profile of the final cheese. However, the selection of a suitable primary starter is imperative to ensure a desirable product.

Tandem sulfur chemiluminescence and flame ionization detection with planar microfluidic devices for the characterization of sulfur compounds in hydrocarbon matrices

The detection of sulfur compounds in different hydrocarbon matrices, from light hydrocarbon feedstocks to medium synthetic crude oil feeds provides meaningful information for optimization of refining processes as well as demonstration of compliance with petroleum product specifications. With the incorporation of planar microfluidic devices in a novel chromatographic configuration, sulfur compounds from hydrogen sulfide to alkyl dibenzothiophenes and heavier distributions of sulfur compounds over a wide range of matrices spanning across a boiling point range of more than 650°C can be characterized, using one single analytical configuration in less than 25min. In tandem with a sulfur chemiluminescence detector for sulfur analysis is a flame ionization detector. The flame ionization detector can be used to establish the boiling point range of the sulfur compounds in various hydrocarbon fractions for elemental specific simulated distillation analysis as well as profiling the hydrocarbon matrices for process optimization. Repeatability of less than 3% RSD (n=20) over a range of 0.5–1000 parts per million (v/v) was obtained with a limit of detection of 50 parts per billion and a linear range of 0.5–1000 parts per million with a correlation co-efficient of 0.998.

Simultaneous Measurement of Hydrocarbons and Sulfur Compounds using Flame Ionization and Sulfur Chemiluminescence Detection for Sulfur Simulated Distillation

A gas chromatographic system for the simultaneous acquisition of hydrocarbon and sulfur chromatograms was developed. Detection of sulfur compounds is achieved using a sulfur chemiluminescence detector (SCD) mounted in series with a flame ionization detector (FID). A constant fraction of the effluent of the FID is transferred to the SCD by means of a fixed restrictor. Unlike previous versions of this approach, the FID is not used to generate the chemiluminescent sulfur species. Rather, the FID is operated under optimum conditions for hydrocarbon analysis and a furnace is used to generate the chemiluminescent sulfur species. The system permits dual acquisition of the hydrocarbon and sulfur signals in a single analysis with a single column, since the detectors are operated in a serial fashion. The application of sulfur simulated distillation using this approach was examined, since this requires simultaneous universal and sulfur selective detection. Precision of absolute response of both the FID and SCD was typically less than 2% RSD for a standard reference material.

Gas chromatography with flame ionization and flameless sulfur chemiluminescence detectors in series for dual channel detection of sulfur compounds

The dual-channel detection of samples with detectors coupled in series is possible only when the first detector is a non-destructive one. However, the configuration where a destructive detector, such as the flame ionization detector (FID), is followed by the flameless, sulfur chemiluminescence detector (flameless SCD) can be used to detect simultaneously carbon and sulfur. In this work, the FID and flameless SCD are coupled in series for dual-channel detection of sulfur compounds in three gasoline samples. Optimum conditions for flameless SCD were evaluated by altering the flow rates of hydrogen and air and the oxygen pressure to the ozone generator. Samples are identified by retention indices where the homologous n-alkylthiols are used as standards. The increment in retention index per carbon number of the n-alkylthiols is 105.54 in the Quadrex 007 series, 0.32 mm i.d., 4 μm film, column.

Chromatographic parameters derived for the non-linear response of a flame photometric detector

A mathematical derivation of efficiency and resolution equations for use in conjunction with flame photometric detection of sulphur compounds is presented. These equations are similar to those for linear detection apart from the incorporation of the exponential response factor, n, in the denominator of the respective expressions for non-linear detection. The latter equations reduce to those usually recognised for linear detection if the value n=1 is substituted. Equating the column efficiency equations for linear and non-linear detection permits direct determination of the value of n.

Detection of Sulphur Compounds on Paper Chromatograms

A METHOD for the qualitative analysis of sulphoxides on paper chromatograms, based on the well-known property of these compounds to oxidize hydroiodic acid to free iodine, has recently been published by Thompson et a1.1. In the course of our work on the metabolism of some sulphur compounds, we had the opportunity, some years ago, to adapt the same reaction to paper chromatography, and to test its specificity over a wide range of cystine and cystamine derivatives2–6.